How to Render a Template without a custom Controller

Usually, when you need to create a page, you need to create a controller
and render a template from within that controller. But if you're rendering
a simple template that doesn't need any data passed into it, you can avoid
creating the controller entirely, by using the built-in FrameworkBundle:Template:template
controller.

For example, suppose you want to render a static/privacy.html.twig
template, which doesn't require that any variables are passed to it. You
can do this without creating a controller:

You can of course also use this trick when rendering embedded controllers
from within a template. But since the purpose of rendering a controller from
within a template is typically to prepare some data in a custom controller,
this is probably only useful if you'd like to cache this page partial (see
Caching the static Template).

Since templates that are rendered in this way are typically static, it might
make sense to cache them. Fortunately, this is easy! By configuring a few
other variables in your route, you can control exactly how your page is cached: